Rotary drilling apparatus

ABSTRACT

Apparatus adapted to be mounted in a rotary drilling drill string. It encompasses an acoustic discontinuity so located relative to the bit as to enhance or inhibit longitudinal vibrations of the bit during drilling operations.

United States Patent 1191 1111 3,815,691

Richter, Jr. et a1. 45 J -11, 1974 ROTARY DRILLING APPARATUS 2,554,005 5/1951 2.858,l08 10/1958 [75] Inventors: Albert P. Rlchter, Jr., Houston, 2,942,849 M960 Tex.; James D. Bruner, Englewood, 2,989,130 6/1961 Colo; Roy P. Mazzagatti, Bellaire; 3,99 9 3 Hugh E. Hall, Jr., Huntsville, both 3,139,146 6/1964 of Tex. 3,307,641 3/1967 [73] Ass1gnee: Texaco Inc., New York, NY. Primary Examiner Emest R- Purser Filedl J n- '19, 1972 Assistant ExaminerRichard E. Favreau [21 I Appl- Nm 219 on Attorney, Agent, or FirmT. H. Whaley; C. G. Reis 52 us. c1. 175/56, 175/320 [57] ABSTRACT 51 Int. (:1 B06b 1/00 Apparatus adapted to be mounted in a r ry drilling 58 Field f Search 175 5 55 57; 4/27 N drill string. It encompasses an acoustic discontinuity so located relative to the bit as to enhance or inhibit [56] R fe Cit d longitudinal vibrations of the bit during drilling opera- UNITED STATES PATENTS floris- 2,325.132 7/1943 Haushalter et al 175/56 14 Claims, 7 Drawing Figures ROTARY DRILLING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns rotary drilling in general, and more specifically relates to a combination for use in rotary drilling that permits the use of natural vibrations which develop during drilling procedure.

2. Description of the Prior Art Heretofore, various suggestions and arrangements have been made which involved superimposed vibrations on rotary drilling operations. This was usually done by applying eccentric weights, usually located at the surface and causing longitudinal vibration in the drill string. Another procedure involved application of fluid pressure waves developed in the drilling fluid, in order to create vertical vibration and similar high frequency effects at the drill bit. In actual rotary drilling operation, however, neither of the former arrangements have proved satisfactory.

Consequently, it is an object of this invention to provide a structurally simple, yet highly effective means for taking advantage of natural vibratory or acoustic energies which develop in a drill string during drilling with rotary-type equipment.

SUMMARY OF THE INVENTION Briefly, this invention concerns rotary drilling that employs a drill string having a bit attached at the bottom thereof. The said drill string produces a natural resonance when drilling which has a standing wave length equal to the length of an average joint of drill collars in said string. It relates to the improvement which comprises sub means for connecting said bit onto said drill string. The said sub means includes an acoustic discontinuity located at a predetermined dis? tance from said bit whereby the location of said bit relative to said standing wave may be controlled.

Again, briefly, the invention concerns an acoustic sub for use in rotary drilling and adapted for mounting between the bit and drill collars section of a drill string. It comprises an acoustic discontinuity located a predetermined distance from the bit end of the said sub. The said predetermined distance is related to the wave length of a natural resonant acoustic frequency of said drill string for obtaining a desired tendency to produce more or less longitudinal vibrations in the bit when drilling. The said degree of vibration is determined as desired for a given formation that is to be encountered.

BRIEF DESCRIPTION OF THEDRAWINGS The foregoing and other objects and benefits of the invention will be more fully set forth below in connection with the best mode contemplated by the inventor of carrying out the invention, and in connection with which there are illustrationsfprovided in the drawings, wherein: f

FIG. 1 is a schematic illustration showing a drill string which includes therein elements of this invention;

FIG. 2 is a schematic showing in cross-section illus- FIGS. 4-7 are illustrations showing cross sectional schematic views, along with the applicable graph in each case indicating the standing wave vibrations in a tuned sub section of the drill string.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In orderto assist with an understanding of this invention, and for clarity in defining the scope thereof, the following definitions are provided. It may be noted that these definitions are commonly employed in the practice of deep-well rotary drilling.

Drill String A total assembly of the elements employed in deep-well rotary drilling which are supported from a surface structure while being rotated during the drilling process.

Drill Pipe That portion of the drill string which is made up of drill pipe joints. These are usually thirty to forty-five feet long and have about 1% to 3 4 inch wall thickness. This portion of the drill string is usually in tension loading during the drilling operation. These joints are located in the upper portion of the drill string between the rig floor and the lower sections of the string. At any substantial depth, the drill pipe constitutes a major length of the drill string.

Drill Collars That portion of the drill string which is made up of drill collar joints. These are usually thirty to forty-five feet long and have about 2 to 3 inch wall thickness. They are located at at the bottom end of the drill string between the drill pipe and a drill bit (defined below). This portion of the drill string is usually in compression loading during the drilling operation. Drill collars provide mass at the lower end of the drill string which achieves the desired weight on the bit, tensionloading in the drill pipe (to prevent buckling), and stabilization of the drill bit (to insure the-drilling of a straight hole). The overall length of a drill collar section may be about 200 to 500 feet.

Drill String Sub A short length of pipe, usually two to six feet long. Such unit has the necessary tool joints (defined below) at each end in order to couple dissimilar types of threads.

Tool Joints The threaded section at each end of a drill pipe, drill collar or sub. A tool joint usually is welded onto drill pipe", but it is most often machined directly onto drill collars and subs.

Drill Bit A device at the bottom end of the drill string which performs the drilling of the earth formations.

It will be clear from the foregoing that a drill string is the total assembly of drill bit, necessary subs, drill collars" and drill pipe.

It has been discovered that during rotary drilling operations, and particularly where the well being drilled has substantial depth, a standing acoustic wave tends to develop in the drill string. Such standing wave has'a wave length equal to the average length of the drill pipe and/or drill collars that are being employed. This led to the invention whereby it becomes feasible to control the degree of longitudinal vibration that is generated at the bit.

It will be appreciated that when drilling in relatively soft materials, the efficiency will be enhanced if the drill bit maintains continuous contact with the formation being drilled, that is without any longitudinal vibration. On the other hand, in hard formations just the opposite is desired in that some vertical impacting helps to increase the drilling rate. By making use of the invention, either condition may be maximized by merely determining the type of formation to be drilled and applying the principles of the invention so as to either minimize or maximize the longitudinal vibration which will be generated at the drill bit by the natural resonant conditions.

Referring to FIG. 1, it will be observed that the illustration schematically shows the elements which go to make up a complete drill string 11. Starting at the upper end and going down, there is a section of drill pipe 12 followed by one or more sections of drill collars, e.g., a section 13 and section 14. At the lower end of the drill collar section 14, there is a special section 15 in accordance with the invention, with a drill bit 16 attached at the lower end thereof. As will appear more fully hereafter, the special section 15 may be designed for providing either a maximum or minimum longitudinal acoustic energy vibration at the bit 16. The maximum vibration is preferable for hard rock formations, while the minimum vibration is more efficient for soft formation drilling.

FIG. 2 illustrates schematically only the lower end of a drill string. It illustrates a combination that employs a compliant sub 21 that is connected into the drill string at the lower end of a bottom-most collar 22. This collar 22 is attached to the sub 21 by the usual tool joints 25 and 26. Then, below the compliant sub 21, there is a special or tuned sub which is attached to the compliant sub by means of a joint 31, Finally, there is a bit 32 attached to the lower end of the tuned sub 30. As will appear in greater detail below, the length of the special or tuned sub 30 (including its joint 31) will be designed to have a length such that a desired condition of maximum or minimum longitudinal acoustic vibration will occur at the bit 32 during drilling.

.FIG. 3 illustrates another embodiment of the invention. It employs a noncompliant sub 36 which is located at the lower end of a drill collar 37. Beneath the sub 36, there is attached a special or tuned sub 38 to which a bit 39 is attached. In this case, again, the length of the tuned sub 38 is designed to create a desired condition during drilling, which is either maximum or minimum longitudinal vibration by th'e'bit 39. The principles involved are discussed in greater detail below in relation to FIGS. 4-7.

It will be observed that the compliant sub 21 (FIG.

2) is constructed with thinner walls than the adjacent elements of the drill string so that it becomes analogous to a laterally supported coil spring, which permits longitudinal movements. On the other hand, the opposite is true with respect to the noncompliant sub 36 (FIG. 3) which has a thicker wall structure than the adjacent drill-string elements. It acts as a stiffener or opposite type of acoustic discontinuity in the drill string, compared to the compliant sub 21.

The manner in which the invention acts to create desired longitudinal, i.e., acoustic vibratory motion at the bit, will be more fully explained in connection with FIGS. 4-7. These figures include graphs for illustrating the vibratory conditions.

Thus, FIG. 4 schematically illustrates a compliant sub 45 located between the lower end of a drill collar 46 and the upper end of the special or tuned sub 47. A drill bit 48 is attached at the Iowe end of the sub 47.

It will be appreciated that the compliant sub 45 acts as an acoustic discontinuity in the drill string. Also, as

4 indicated above, the length of a standing-wave acoustic-energy resonant frequency will coincide with the length of an average drill collar. Therefore, as indicated by a graph 51 in FIG. 4, the length of the special or tuned sub 47 may be made such that there is a onequarter wave length distance from the middle of the compliant sub 45 to the bit 48. Consequently, the bit location corresponds with a point 52 on the ordinate of the graph 51 which represents a node for the standing acoustic wave. At the other end of the special sub 47 the compliant sub 45 will encourage maximum longitudinal acoustic-energy vibrations. This is indicated by another point 53 on the ordinate of the graph. It will be observed that there is a curve 56 shown on the graph which represents the vertical vibratory displacement along the abscissa of the graph.

It will be also noted that while the curve 56 of FIG. 4 illustrates a one-quarter wave-length condition, similar results may be accomplished by employing any oddnumbered fractions of one-quarter wavelength distances. Thus, the tuned sub 47 might be designed to have lengths so as to correspond with wave lengths equal 'to one-quarter, three-quarters, five-quarters, etc., of the basic acoustic standing wave length. These conditions will create minimum vertical vibratory movement by the bit 48, and such conditions would be best employed for maximum drilling rate where the formation being drilled is soft.

FIG. 5 illustrates another modifiction which employs a compliant sub. In this case there is a compliant sub 60 that is connected beneath a drill collar 61. Attached beneath the compliant sub 60 is a tuned sub 62, and thereis a bit 63 at the lower end of the sub 62. As illustrated in an accompanying graph 66, this will provide maximum vibratory movement of the bit 63. In this case, the length of the sub 62 will be made so as to conform with conditions illustrated by the graph 66. There is an ordinate 67 and an abscissa 68 for showing the conditions of vertical displacement (parallel to the abscissa 68) relative to the longitudinal location of the elements in the drill string (parallel to the ordinate 67). These resonant conditions are indicated by a curve 71. It will be noted that there is a point 72 on the ordinate 67 which represents the location of a node of the standing wave acoustic energy.

In this case, by having the longitudinal distance between the bit 63 and the compliant sub 60 equal to even-numbered one-quarter wavelengths of the standing wave, there will be a maximum vibratory vertical movement by the bit along with such motion in the compliant sub. Consequently, this set of conditions would be especially applicable to hard rock type formations, in order to obtain maximum drilling rate.

Referring to FIGS. 6 and 7, it will be appreciated that similar conditions as described with respect to FIGS. 4 and 5, may be accomplished by using the opposite type of acoustic discontinuity, i.e., a noncompliant sub. Thus, in FIG. 6, there is illustrated a noncompliant sub 76 attached at the lower end of a drill collar 77, and there is a special sub 78 connected beneath the noncompliant sub 76 with a bit 79 attached at the bottom of the special sub 78.

The conditions which FIG. 6 illustrates are accomplished by having the tuned or special sub 78 designed with the proper length. As before, the illustration includes a graph 82 that applies to the schematically shown elements of the drill string indicated in FIG. 6.

In this case, there are two nodes developed at a point 83 on an ordinate 84 of the graph, as well as at another point 85 thereon. These conditions will be developed by having the length of the tuned sub 78 such as to separate the bit 79 from the noncompliant sub 76 an evennumbered one-quarter wave length apart. This is, of course, illustrated by a curve 86. The same explanations concerning wave length, etc., as indicated above with respect to FIGS. 4 and 5, apply here and need not be repeated.

FIG. 7 illustrates an arrangement for obtaining conditions like those described in relation to P16. 5. However, in this case there is a noncompliant sub 91 at the lower end of a drill collar 92 and connected to the top of a special or tuned sub 93. Then there is, of course, a bit 94 attached to the bottom of the tuned sub 93. The conditions that are developed by this arrangement are illustrated by a graph 98 which has a curve 99 shown relative to an ordinate 100, and an abscissa 101. The design is such as to have the length of the special sub 93 create conditions shown by the graph 98. Thus, the distance between a node 104 (at noncompliant sub 91) on the curve and an antinode 105 at the bit 94 will be equal to an odd-numbered one-quarter wave length of the resonant standing wave that tends to develop in the drill string during drilling, as has been described above. Therefore, this modification or arrangement of the elements in a drill string will give results which are especially beneficial in hard rock formation drilling.

It may be noted that the invention entails a structurally simple arrangement that is very effective and extremely practical for obtaining substantial improvement in drilling rates with standard rotary drilling procedures.

While particular embodiments of the invention have been described above in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention, but merely as being descriptive thereof.

What we claim is:

1. ln rotary drilling, in combination with a conventional drill string having a bit attached at the bottom thereof, said conventional string comprising plural sections of drill pipe and drill collars having an average length between joints thereof and producing a natural resonance therein when drilling, said natural resonance having a standing wave length equal to the length of an average joint of drill collars in said string, the improvement comprising acoustic sub means for connecting said bit onto said drill string,

said sub means including an acoustic discontinuity which comprises a section of said sub having a mass substantially different from the mass of an equal length section of the adjacent drill collar, and

said discontinuity being located a predetermined distance from said bit whereby the location of said bit relative to said standing wave in said conventional drill string may be controlled.

2. The invention according to claim 1, wherein said sub means is constructed of material similar to the material of said drill string,

and said discontinuity section is constructed with wall thickness substantially different from the wall thickness of said adjacent drill collar.

3. The invention according to claim 2, wherein said discontinuity section is constructed with wall thickness substantially less than that of said adjacent drill collar.

4. The invention according to claim 3, wherein said predetermined distance for locating said discontinuity section from said bit is an odd multiple of one-quarter of said standing wave length.

5. The invention according to claim 3, wherein said predetermined distance for locating said discontinuity section from said bit is an even multiple of one-quarter of said standing wave length.

6. The invention according to claim 2, wherein said discontinuity section is constructed with wall thickness substantially more than that of said adjacent drill collar.

7. The invention according to claim 6, wherein said predetermined distance for locating said discontinuity section from said bit is an even multiple of one-quarter of said standing wave length.

8. The invention according to claim 6, wherein said predetermined distance for locating said discontinuity section from said bit is an odd multiple of one-quarter of said standing wave length.

9. The invention according to claim 1, wherein said discontinuity has a mass substantially less than that of said equal length section of said drill collar.

10. The invention according to claim 9, wherein said predetermined distance for locating said discontinuity is an odd multiple of one-quarter of said standing wave length.

11. The invention according to claim 9, wherein said predetermined distance for locating said discontinuity is an even multiple of one-quarter of said standing wave length.

12. The invention according to claim 1, wherein said discontinuity has a mass per unit length which is substantially more than that of said drill collar.

13. The invention according to claim 12, wherein said predetermined distance for locating said discontinuity is an even multiple of one-quarter of said standing I wave length. 

1. In rotary drilling, in combination with a conventional drill string having a bit attached at the bottom thereof, said conventional string comprising plural sections of drill pipe and drill collars having an average length between joints thereof and producing a natural resonance therein when drilling, said natural resonance having a standing wave length equal to the length of an average joint of drill collars in said string, the improvement comprising acoustic sub means for connecting said bit onto said drill string, said sub means including an acoustic discontinuity which comprises a section of said sub having a mass substantially different from the mass of an equal length section of the adjacent drill collar, and said discontinuity being located a predetermined distance from said bit whereby the location of said bit relative to said standing wave in said conventional drill string may be controlled.
 2. The invention according to claim 1, wherein said sub means is constructed of material similar to the material of said drill string, and said discontinuity section is constructed with wall thickness substantially different from the wall thickness of said adjacent drill collar.
 3. The invention according to claim 2, wherein said discontinuity section is constructed with wall thickness substantially less than that of said adjacent drill collar.
 4. The invention according to claim 3, wherein said predetermined distance for locating said discontinuity section from said bit is an odd multiple of one-quarter of said standing wave length.
 5. The invention according to claim 3, wherein said predetermined distance for locating said discontinuity section from said bit is an even multiple of one-quarter of said standing wave length.
 6. The invention according to claim 2, wherein said discontinuity section is constructed with wall thickness substantially more than that of said adjacent drill collar.
 7. The invention according to claim 6, wherein said predetermined distance for locating said discontinuity section from said bit is an even multiple of one-quarter of said standing wave length.
 8. The invention according to claim 6, wherein said predetermined distance for locating said discontinuity section from said bit is an odd multiple of one-quarter of said standing wave length.
 9. The invention according to claim 1, wherein said discontinuity has a mass substantially less than that of said equal length section of said drill collar.
 10. The invention according to claim 9, wherein said predetermined distance for locating said discontinuity is an odd multiple of one-quarter of said standing wave length.
 11. The invention according to claim 9, wherein said predetermined distance for locating said discontinuity is an even multiple of one-quarter of said standing wave length.
 12. The invention according to claim 1, wherein said discontinuity has a mass per unit length which is substantially more than that of said drill collar.
 13. The invention according to claim 12, wherein said predetermined distance for locating said discontinuity is an even multiple of one-quarter of said standing wave length.
 14. The invention according to claim 12, wherein said predetermined distance for locating said diScontinuity is an odd multiple of one-quarter of said standing wave length. 